A "locomotive going by sound" has developed when you start the car. on 2005 Hyundai Elantra

It's not every start, but there getting more often. I've checked airbox integrity, all vacuum hoses, connections under the hood, etc.

Asked by for the 2005 Hyundai Elantra
Would you mind giving us a call to further discuss this noise. Please call 972-221-5678. Thanks, Ernie